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Chapter 6: The Traditional Approach to Requirements

Chapter 6: The Traditional Approach to Requirements. Systems Analysis and Design in a Changing World, 3 rd Edition. Learning Objectives. Explain how the traditional approach and the object-oriented approach differ when an event occurs

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Chapter 6: The Traditional Approach to Requirements

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  1. Chapter 6:The Traditional Approach to Requirements Systems Analysis and Design in a Changing World, 3rd Edition

  2. Learning Objectives • Explain how the traditional approach and the object-oriented approach differ when an event occurs • List the components of a traditional system and the symbols representing them on a data flow diagram • Describe how data flow diagrams can show the system at various levels of abstraction Systems Analysis and Design in a Changing World, 3rd Edition

  3. Learning Objectives (continued) • Develop data flow diagrams, data element definitions, data store definitions, and process descriptions • Develop tables to show the distribution of processing and data access across system locations • Read and interpret Information Engineering models that can be incorporated within traditional structured analysis Systems Analysis and Design in a Changing World, 3rd Edition

  4. Overview • What the system does what an event occurs: activities and interactions • Traditional structured approach to representing activities and interactions • Diagrams and other models of the traditional approach • RMO customer support system example shows how each model is related • How traditional and IE approaches and models can be used together to describe system Systems Analysis and Design in a Changing World, 3rd Edition

  5. Traditional and Object-Oriented Views of Activities Systems Analysis and Design in a Changing World, 3rd Edition

  6. Requirements Models for the Traditional and OO Approaches Systems Analysis and Design in a Changing World, 3rd Edition

  7. Data Flow Diagrams • Graphical system model that shows all main requirements for an IS in one diagram • Inputs / outputs • Processes • Data storage • Easy to read and understand with minimal training Systems Analysis and Design in a Changing World, 3rd Edition

  8. Data Flow Diagram Symbols Systems Analysis and Design in a Changing World, 3rd Edition

  9. DFD Fragment from the RMO Case Systems Analysis and Design in a Changing World, 3rd Edition

  10. DFD Integrates Event Table and ERD Systems Analysis and Design in a Changing World, 3rd Edition

  11. DFD and Levels of Abstraction • Data flow diagrams (DFDs) are decomposed into additional diagrams to provide multiple levels of detail • Higher level diagrams provide general views of system • Lower level diagrams provide detailed views of system • Differing views are called levels of abstraction Systems Analysis and Design in a Changing World, 3rd Edition

  12. Layers of DFD Abstraction Systems Analysis and Design in a Changing World, 3rd Edition

  13. Context Diagrams • DFD that summarizes all processing activity • Highest level (most abstract) view of system • Shows system boundaries • System scope is represented by a single process, external agents, and all data flows into and out of the system Systems Analysis and Design in a Changing World, 3rd Edition

  14. DFD Fragments • Created for each event in the event table • Represents system response to one event within a single process symbol • Self contained model • Focuses attention on single part of system • Shows only data stores required to respond to events Systems Analysis and Design in a Changing World, 3rd Edition

  15. DFD Fragments for Course Registration System Systems Analysis and Design in a Changing World, 3rd Edition

  16. Event-Partitioned System Model • DFD to model system requirements using single process for each event in system or subsystem • Decomposition of the context level diagram • Sometimes called diagram 0 • Used primarily as a presentation tool • Decomposed into more detailed DFD fragments Systems Analysis and Design in a Changing World, 3rd Edition

  17. Combining DFD Fragments Systems Analysis and Design in a Changing World, 3rd Edition

  18. Context Diagram for RMO Customer Support System Systems Analysis and Design in a Changing World, 3rd Edition

  19. RMO Subsystems and Events Systems Analysis and Design in a Changing World, 3rd Edition

  20. Context Diagram for RMO Order-Entry Subsystem Systems Analysis and Design in a Changing World, 3rd Edition

  21. DFD Fragments for RMO Order-Entry System Systems Analysis and Design in a Changing World, 3rd Edition

  22. Decomposing DFD Fragments • Sometimes DFD fragments need to be explored in more detail • Broken into subprocesses with additional detail • DFD numbering scheme: • Does not equate to subprocess execution sequence • It is just a way for analyst to divide up work Systems Analysis and Design in a Changing World, 3rd Edition

  23. Physical and Logical DFDs • Logical model • Assumes implementation in perfect technology • Does not tell how system is implemented • Physical model • Describes assumptions about implementation technology • Developed in last stages of analysis or in early design Systems Analysis and Design in a Changing World, 3rd Edition

  24. Detailed Diagram for Create New Order Systems Analysis and Design in a Changing World, 3rd Edition

  25. Physical DFD for scheduling courses Systems Analysis and Design in a Changing World, 3rd Edition

  26. Evaluating DFD Quality • Readable • Internally consistent • Accurately represents system requirements • Reduces information overload: Rule of 7 +/- 2 • Single DFD should have not more than 7 +/-2 processes • No more than 7 +/- 2 data flows should enter or leave a process or data store on a single DFD • Minimizes required number of interfaces Systems Analysis and Design in a Changing World, 3rd Edition

  27. Data Flow Consistency Problems • Differences in data flow content between a process and its process decomposition • Data outflows without corresponding inflows • Data inflows without corresponding outflows • Results in unbalanced DFDs Systems Analysis and Design in a Changing World, 3rd Edition

  28. Consistency Rules • All data that flows into a process must: • Flow out of the process or • Be used to generate data that flow out of the process • All data that flows out of a process must: • Have flowed into the process or • Have been generated from data that flowed into the process Systems Analysis and Design in a Changing World, 3rd Edition

  29. Unnecessary Data Input: Black Hole Systems Analysis and Design in a Changing World, 3rd Edition

  30. Process with Impossible Data Output: Miracle Systems Analysis and Design in a Changing World, 3rd Edition

  31. Process with Unnecessary Data Input Systems Analysis and Design in a Changing World, 3rd Edition

  32. Process with Impossible Data Output Systems Analysis and Design in a Changing World, 3rd Edition

  33. Documentation of DFD Components • Lowest level processes need to be described in detail • Data flow contents need to be described • Data stores need to be described in terms of data elements • Each data element needs to be described • Various options for process definition exist Systems Analysis and Design in a Changing World, 3rd Edition

  34. Structured English • Method of writing process specifications • Combines structured programming techniques with narrative English • Well suited to lengthy sequential processes or simple control logic (single loop or if-then-else) • Ill-suited for complex decision logic or few (or no) sequential processing steps Systems Analysis and Design in a Changing World, 3rd Edition

  35. Structured English Example Systems Analysis and Design in a Changing World, 3rd Edition

  36. Process 2.1 and Structured English Process Description Systems Analysis and Design in a Changing World, 3rd Edition

  37. Decision Tables and Decision Trees • Can summarize complex decision logic better than structured English • Incorporates logic into the table or tree structure to make descriptions more readable Systems Analysis and Design in a Changing World, 3rd Edition

  38. Decision Tree for Calculating Shipping Charges Systems Analysis and Design in a Changing World, 3rd Edition

  39. Data Flow Definitions • Textual description of data flow’s content and internal structure • Often coincide with attributes of data entities included in ERD Systems Analysis and Design in a Changing World, 3rd Edition

  40. Data Element Definitions • Data type description • e.g. string, integer, floating point, Boolean • Sometimes very specific • Length of element • Maximum and minimum values • Data dictionary – repository for definitions of data flows, data stores, and data elements Systems Analysis and Design in a Changing World, 3rd Edition

  41. Components of a Traditional Analysis Model Systems Analysis and Design in a Changing World, 3rd Edition

  42. Information Engineering Models • Focuses on strategic planning, enterprise size, and data requirements of new system • Shares features with structured system development methodology • Developed by James Martin in early 1980’s • Thought to be more rigorous and complete than the structured approach Systems Analysis and Design in a Changing World, 3rd Edition

  43. Information Engineering System Development Life Cycle Phases Systems Analysis and Design in a Changing World, 3rd Edition

  44. Process Decomposition and Dependency Models • IE process models show three information types • Decomposition of processes into other processes • Dependency relationships among processes • Internal processing logic • Process decomposition diagram – represents hierarchical relationship among processes at different levels of abstraction • Process dependency model – describes ordering of processes and interaction with stored entities Systems Analysis and Design in a Changing World, 3rd Edition

  45. Process Dependency Diagram Systems Analysis and Design in a Changing World, 3rd Edition

  46. Process Dependency Diagram with Data Flows Systems Analysis and Design in a Changing World, 3rd Edition

  47. Locations and Communication Through Networks • Logical information needed during analysis • Number of user locations • Processing and data access requirements at various locations • Volume and timing of processing and data access requests • Needed to make initial design decisions such as: • Distribution of computer systems, application software, database components, network capacity Systems Analysis and Design in a Changing World, 3rd Edition

  48. Gathering Location Information • Identify locations where work is to be performed • Draw location diagram • List functions performed by users at each location • Build activity-location matrix • Rows are system activities from event table • Columns are physical locations • Build Activity-data (CRUD) matrix • CRUD – create, read, update, and delete Systems Analysis and Design in a Changing World, 3rd Edition

  49. RMO Location Diagram Systems Analysis and Design in a Changing World, 3rd Edition

  50. RMO Activity-Location Matrix Systems Analysis and Design in a Changing World, 3rd Edition

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